The endothelial and inducible nitric oxide synthases (eNOS and iNOS) have key regulatory roles in both normal vascular physiology and in vascular pathology. Preliminary studies presented in this proposal indicate that eNOS interacts directly with the bradykinin B2 receptor and with the CAT1 cationic amino acid transporter in vascular endothelial cells. In addition, it has been shown that iNOS is coinduced with the CAT2 cationic amino acid transporter in vascular smooth muscle cells. Because iNOS and CAT2 are structurally and functionally very similar to eNOS and CAT1, we postulate that iNOS and CAT2 also interact in smooth muscle. In this application, we propose to test the hypothesis that eNOS is regulated in endothelial cells by inhibitory interactions with the B2 receptor. We will also determine the role of tyrosine phosphorylation in regulation of the interaction and will define the domains in the two proteins that are responsible for the interaction. We further propose to test the hypothesis that the eNOS-CAT1 interaction facilitates NO release from endothelial cells and will determine what the interacting domains are in the two proteins. Finally, we will test the hypothesis that the iNOS-CAT2 interaction facilitates NO release from vascular smooth muscle cells and will define the domains in the two proteins that are involved in the interaction.